Electrosensitive stencil blank



March 14, 1950 R. J. Mass 2,500,617

ELECTROSENSITIVE STENCIL BLANK Filed Aug. 4, 1942 T FIG. I R l4 I3 III as 31 35 H 24 Al A2 5'" 1' 1 r \e 1'; 2s 29 1i n; 3a

N 17 is i I 37 FIG. 3

lNVENTOR CONDUCTING 'R..J.MEIG.S STENCIL ATTORN EY B L A N K BY Mama Patented Mar. 14, 1950 ELECTROSENSITIVE STENCIL BLANK Return J. Meigs, Westfield, N. J., assignor to Th Western Union Telegraph Company, New York, N. r., a corporation of New York Application August 4, 1942, Serial No. 453,604

1 Claim. 1

This invention relates generally to an electrosensitivestencil blank and method of forming the same for reproducing copies of writing, pictures, drawings and other subject matter, and more particularly to an improved electrosensitive stencil blank and a method of recording thereon for preparing a master copy of subject matter, which may be in facsimile or otherwise, from which numerous copies may be made by the Mimeograph, hectograph, or other reproducing process.

Heretofore in the cutting of stencils and the like for the purpose of reproducing thereon, as a facsimile, writing, pictures or other subject matter, such stencils usually have been cut on standard commercial stencil papers by the mechanical action of a scanning stylus operated electromag netically so as intermittently to engage the stencil paper in a direction substantially normal to the plane of the paper. Such stencil paper, as is well-known, usually consists of a sheet of an open-texture paper, such as yoshino paper, which has unusually long fibers and a somewhat open and porous structure, impregnated or coated with a soft mixture of oils, resin, waxes and the like. The impact of the stylus as it scans the stencil sheet causes this impregnant or coating to be pushed or squeezed aside from the area immediately under the stylus, leaving the longfibers of the porous paper to maintain continuity of the sheet. A stencil sheet on which a recording is thus made is permeable to the stencil ink at those points where the stylus removed the impregnant in accordance with the received pattern and, therefore, is suited for use in making any desired number of copies in the usual manner of Mimeograph stencils. This method of recording on stencil sheets, however, is disadvantageous-because of the fact that the relatively limited speed of operation necessitated by the mechanical action of the stylus is unsatisfactory above its own limits of speed, and therefore such a method is undesirably limited with respect to the recording speed at which the stylus cutting device could satisfactorily be operated. Moreover, with the prior method above referred to, the amplitude of the stylus swing and the frequency response characteristic of such a recording unit does not have the desired uniformity when producing stencils of the character set forth.

One of the objects of the present invention is a stencil sheet from which a stencil may be formed satisfactorily at a rate such that the linear scanning speed at which the stencil form ing device travels may be greatly increased and thus appreciably reduce the time required for producing a. stencil comprising a. given piece of subject matter, while at the same time an exceedingly fine andsharpdefinition of the recorded subject matter is obtainable. Where the signals for operating. the stencil-forming instrumentality. are transmitted over commercial telegraph circuits, as from one city or point to another, any resultant saving in. line time is of great importance, and since, in accordancewith the instant invention, the permissible linear scanning speed of the stencil recording device is considerably higher than. the-linear scanning speed heretofore obtainable in practice with. other types of recorders, this substantially reduces the necessary transmission time with. an appreciable saving in the cost of transmission. Moreover, where a combined transmitter and recorder apparatus is employcd in an. oflice for producing stencils, the time required for producing themmay be reduced, thus substantially increasing the number of stencils which may be produced in a given length of time and also appreciably reducing the cost of preparing such. stencils.

Another object of the invention is to produce satisfactory recordings on stencil sheets= with lower power levels of the signaling. current than that required inthe. operation of. prior devices of the character above referred to.

A further object isa methodof preparing stencils in which the various elemental areas of the stencil sheet which are affectedor formed at any instant may be madeexceedingly small, whereby sharper and improved definition of the subject matter recorded onthe stencil: may be obtained.

Still another object is a stencil sheet adapted for conversion into a stencil by the application thereto of electrical signaling currents which displace an impregnating compound to expose the fibers of a porous sheet in those elemental areas or the sheet through which the signaling currents are caused to pass during a recording operation, without deleteriously affecting the fibers of the sheet.

Additional objects and advantages ofthe present invention will be apparent from the following detailed description, taken in connectionwith the accompanying drawings, in which:

Fig. 1 illustrates diagrammatically a transmitting and receiving system for recording subject matter in facsimile on a stencil sheet embodyingthe present invention;

Fig. 2 is a perspective-view of thestencil sheet Fig. 3 is a perspective view of one form of stencil sheet in accordance with the invention.

Reierring specifically to Fig. l of the drawings, there is shown a facsimile transmitter T comprising a metallic cylinder or platen l2 rotatably supported by a driving shaft l3 which is journaled in any suitable manner in the frame members l4 and i5. During transmission of signals the cylinder is rotated, as by a driving motor it, at a predetermined constant speed in the direction indicated by the curved arrow. The driving motor may be either of the alternating current synchronous type or of the direct current type and may be connected to the driven shaft l3 in any suitable manner, as for example by a driving pulley H and belt 18 which passes around a driven pulley 19 secured to the shaft l3, suitable means being provided to prevent slippage of the belt on the pulleys.

When a transmitter such as illustrated in Fig. 1 is employed, transmission of facsimile signals may be effected in the manner described in Patent No. 2,229,091, issued January 21, 1941, or in Patent No. 2,153,858, issued April 11, 1939, or in any other suitable manner. Briefly, a scanning electrode or stylus 22, whose point bears on the suriace of a transmitting blank 1) bearing conductive characters or other subject matter, is supported by a traveling carriage 23 adapted for longitudinal movement along the cylinder l2 to provide the proper number of scanning lines per inch of the subject matter on the blank. The stylus 22 is caused to traverse the cylinder by means 01' a rotatable threaded shaft 24 geared to the cylinder shaft l3, and therefore the stylus point will describe a helical path as the cylinder I2 is rotated and thus produce a scanning action to scan successively the various elemental areas of the subject matter appearing on the surface of the transmitting blank. The method of obtaining the scanning movement described above is well-known, as are various other methods of scanning a given piece of subject matter.

As illustrated, the transmitting stylus 22 is connected by means of a conductor 30 to an amplifier Al, and the metallic drum I2 is connected by means of a brush 25 to the conductor 29 which is also in the circuit of the amplifier Al If desired, the transmitted signals may have a carrier frequency component introduced by the transformer 26, which is connected in series with the lead 29 in the transmitting drum circuit. The transmitter T and recorder B may be physically connected to form a combined transmitterrecorder unit or, as indicated by the broken lines L, the transmitter may be located at a point remote from the recording apparatus R.

At the receiving end, the recording may be effected by any apparatus suitable for the purpose. As illustrated, this apparatus comprises a second amplifier A2 for applying suitable facsimile impulses having a desired signal level to the recording apparatus. The recorder shows one arrangement and method for recording upon a stencil blank s embodying the present invention and comprises a rotatable cylinder or platen 3| of substantially the same diameter as the cylinder of the transmitter T. The cylinder 3| is rotated in synchronism with the transmitting cylinder I2 in any suitable manner, as by means of an alternating current synchronous motor 32 or other kind of motor which is kept in step with the transmitting motor [6 by any of the various known methods of obtaining synchronism.

The recording stencil s is secured to the cylinder 3! in any suitable manner so that it may be traversed by the point of the scanning stylus 33. The stylus 33 is mounted on a traveling carriage 34 and is caused to traverse the recording cylinder in a longitudinal direction by means of the threaded shaft 35 which is geared to the recording drum driving mechanism to provide proper line feed of the scanning unit. As is well-known, the threaded shaft 35 in combination with the rotation of the cylinder 31 produces the scanning action of the stylus 33 to scan successively the various elemental areas of the stencil sheet in the manner in which the scanning action is effected at the transmitting end.

It is to be understood that the specific types of facsimile transmitting mechanism above referred to are illustrative only, since any suitable manner of producing facsimile signals may be employed such, for example, as the optical pick-up apparatus shown in Patent No. 2,158,391, issued May 16, 1939. Similarly, any suitable form of facsimile receiving scanning apparatus may be employed to form a stencil in accordance with the instant invention so long as the stencil sheet is properly scanned, and the proper electrical potentials or currents are selectively applied to the elemental recording areas thereof.

Fig. 2 of the drawings illustrates another method of preparing the stencil sheet s, which in this case is retained in flat condition on a platen 42 of metal or other conducting material that serves as a support for the stencil sheet during the recording operation. A stylus 43, which is carried by a pencil 44, is movable manually so that it may be caused to trace any desired subject matter to be recorded, the platen 42 and the stylus 43 being connected by means of conductors 45 and 46 to a suitable source of marking current 48, so that current or the electrical forces produced thereby are caused to pass or be exerted through the stencil sheet s at just the points where the point of the stylus 43 is caused to contact the surface of the stencil sheet.

A stencil sheet s embodying the invention is shown in Fig. 3 of the drawings. This stencil sheet, which in the form illustrated is adapted to produce a, Mimeograph stencil, preferably comprises a sheet of long-fiber yoshino paper or the like that forms the body portion of the stencil, this sheet being impregnated with a soft stencilforming compound or impregnation, for example, waxy materials, such as paraffin or diglycol stearate, or cellulose acetate, nitrocellulose and other cellulose esters, ethyl cellulose, natural or synthetic resins or gums, such as shellac, rosin, ester gum, cumar, dammar and other well-known varnish gums, or water-sewelling colloids, such as starch, gelatin, pectin and gum tragacanth, or other suitable stencil impregnating materials known in the art. Preferably, the impregnation employed is plasticized by a suitable high boiling compound such, for example, as triphenyl phosphate, triacetin, castor oil, tricresyl phosphate and the like. These impregnating materials are mixed with an electrically conductive substance such as, for example, finely divided carbon particles or a metal powder, the conducting substance or particles being present in an amount suflicient to make the stencil impregnation and the paper base electrically conducting to enable the marking currents readily to pass by current conduction through the stencil sheet between the point of the stylus and the platen on which the sheet is supported without injury to the fibers of the paper sheet, and these marking currents cause the impregnation to be displaced at the precise point of contact of the stylus with the stencil sheet at the time the marking currents are applied thereto, and thus expose the thin paper base to make it pervious to the stencil ink at these points. This displacement of the impregnation appears to be induced by electrostatic action due to the charges formed on the conducting particles which are mixed with the impregnation, although I do not wish to be limited to this explanation, since there maybe other factors involved such as volatilization of products formed as a result of electro-chemical reaction. The impregnation is displaced or deformed cleanly and sharply at the precise points where the marking currents are caused to pass through the conducting paper and at no other place, and even when the stencil is formed at the higher recording speeds obtainable by the method disclosed herein, the Mimeograph copies made therefrom have a definition at least as fine and sharp as when the stencils are formed by an electromagnetically operated stylus and usually produce better definition than has heretofore been obtainable. There is no evidence of burning or charring of the paper sheet or other deleterious effect on the fibers thereof, and the exposed elemental areas of the paper sheet are clean and readily pass the stencil ink when applied thereto in the usual manner of making Mimeograph copies from a stencil.

The rate at which recording may be effected on the stencil sheet is approximately twice the rate heretofore obtainable with an electromagnetically operated stylus and, in fact, can proceed at as fast a rate as is obtainable with electro-chemical recording papers, such as of the type disclosed in Patent No. 2,251,742. Stencils in accordance with the invention have been formed with a linear scanning speed of the recording stylus of the order of 1440 inches per minute and higher, when using a recording drum with a circumference of approximately eight inches and rotating at a speed of 180 R. P. M. or higher.

The relative proportions of the conducting material and the other solids in the impregnating compound employed may vary within wide limits. In general, it has been found that where the impregnation comprises a gum or resin or one of the cellulose esters, in combination with suitable plasticizers, the proportion of a conducting substance, such as finely divided carbon, may vary from .to 40% of the total impregnation employed, these proportions being by weight. Where metallic conducting material is employed, such as finely divided particles of brass, copper or aluminum, the working range may generally be stated to comprise from 5% to of metallic particles with respect to the total impregnation employed. It will be observed that, in general, the amount of metallic particles employed may be somewhat less than in the case where carbon particles are employed, although the carbon particles give .excellent results and in certain instances are preferred to the metallic particles.

Where the impregnation comprises one of the waxes, for example, diglycol stearate, the amount of carbon particles employed may vary from 5% to 20% with respect to the impregnation, and when metallic particles are employed these percentages may be somewhat less. Excellent results have been obtained when the amount of carbon particles is from to of the gum or resin or cellulose ester composition employed as an impregnation. In the case of waxes, 1 0% 6 to 14% of carbon particles has produced good results.

An impregnation which has proved quite satis factory is a highly plasticized cellulose nitrate composition such as disclosed in Patent No. 1,526,- 982, granted February 17, 1925. To this impregnation is added a suitable amount of finely divided carbon, preferably 35% by weight. The carbon may be added to the impregnation by grinding the carbon particles into the impregnation, thereby insuring uniform dispersion of the particles throughout the impregnation and the paper to which the impregnating material is applied, the application of the resultant conducting impregnation being effected in the manner disclosed in Patent No. 1,526,982 for coating or impregnating the yoshino paper base, or may be applied in any other suitable manner known in the impregnating and coating art.

Another example of an impregnation suitable for use with the present invention is a cellulose acetate similar to that disclosed in Patent No. 1,795,461, issued March 10, 1931. In this connection, the following formula has been found satisfactory, it being understood that the formula ma be varied within considerable liimts, and that the following proportions by weight are given as examples only:

In a formula such as the foregoing in which plasticizers are employed, the amount of plasticizer used is generally about 50% by weight of the solid content of the impregnating compound in order to render the compound sufficiently plastic at ordinary temperatures to enable ready displacement of the impregnating compound when subjected to the marking potentials without damaging the fibers of the sheet. Various known plasticizers other than those specifically mentioned herein may be employed, for example, dibutyl phthalate, dibutyl tartrate, butyl lactate and the like, the nature of the particular plasticizer employed controlling the amount required to make the impregnating compound plastic at ordinary room temperatures.

The desired plasticity of the impregnating compound with which the sheet is impregnated ma readily be determined by ascertaining empirically the hardness of the sheet. This may be done by applying to a rectangular mass, for example, a block moulded or cut to A" x A,, x 1", of the solid impregnating material a load of 650 grams on a small circular i'oot one-eighth inch in diameter and, by means of a dial micrometer or other suitable device, observing the thickness, the initial load being applied for purposes of counteracting any effects due to surface variations. Then, by application of an additional 950 gram load, a second reading is taken of the thickness. From this the hardness may be calculated by standard computation as a percentage. The desirable hardness for the most suitable formulas of impregnation is in the neighborhood .of 50%, with a maximum of about 70%. The following examples will serve to illustrate:

A. The :solids of the above formula, when molded into a block about x A" x 1" and placed under a 650 gram load on a foot oneeighth inch in diameter, gave a thickness reading of 0.215 inch. The thickness under the additional load of 950 grams was then read as 0.120 inch. The percentage hardness is the quotient or Hardness: m 72 In this case inferior or unsatisfactory stencil recordings were obtained.

The apparatus employed to obtain the readings is known as the 'Widney Modulinieter, which is commonly employed for measurement of hard-- ness, penetration, resilience and other similar characteristics.

In the case of a wax, such as the diglycol r stearate mentioned, the addition of plasticizer is unnecessary. However, in the event that harder waxes are used, the addition of plasticizer is d sirable, and in some cases necessary, in order to cause the impregnating compound to remain I substantiall plastic at ordinary temperatures or the temperatures under which the paper is employed, the important consideration in each of these cases being that the impregnating compound be sufiiciently plastic to enable ready dis placement of the compound upon application of the marking potentials or currents without damaging the fibers of the sheet, this ready displacement also facilitating the fine and sharp definition desired. The displacement of the impregnating compound in those areas to which the marking potentials or currents are applied leaves only the thin porous fiber structure of the base sheet so that the marked portions are therefore readily permeable to Mimeograph or other copying ink employed, and without requiring marking potentials or currents of values which in themselves would tend to char or damage the fibrous structure of the sheet. It is to be understood that the displacement of the impregnating compound in the selected elemental areas does not depend upon the melting of the compound under the action of the electrical signalin current, but that it is displaced, apparentl by electrostatic action due to charges impressed on the metallic or carbon particles embodied in the impregnating compound. The forces exerted by the electrostatic charges thus induced on the metallic or carbon particles are comparatively strong and enable the displacement to take place at a very high rate of linear scanning speed during a recording operation so that, as above set forth, a stencil in accordance with the instant invention may be formed substantially at a rate corresponding to the rate at which records may be produced by means of electrosensitive recording paper heretofore known, such as the lead thiosulphate recording paper disclosed and claimed in the Kline Patent No. 2,251,742, issued August 5, 1941.

The yoshino paper or other porous sheet is suitably impregnated with the above formula, which forms a firm layer on evaporation of the three volatile ingredients of the mixture, which are acetone, benzol and alcohol. The impregnating compound may be introduced into the sheet by floating the sheet on the surface of the impregnating bath, or by passing it through the bath, or by transfer from a roller running in the bath, or other known suitable method. In each case, the excess material may be removed by passing the impregnated sheet over a straight edge or doctor blade, or by passing the sheet over a wire-Wound rod, or between two of such devices, or in other suitable manner known in the art. After the volatile contents have evaporated, the stencil sheet will have the same general appearance and form as the usual stencil sheet except that the paper will be opaque and black in color due to the addition of the carbon particles.

When a wax material is employed, it is desirable to employ the method used in the manufacture of typewriter carbon paper, which comprises treating one side of the paper with a molten wax composition and removing the excess by drawing over a wire-wound rod. It will be appreciated that, due to the open texture of the base or sheet, the same will be impregnated rather than merely coated. A suitable mixture is parts of diglycol. stearate and 12 parts of carbon.

In the foregoing specific examples given it will be appreciated that the relative proportions ma be varied, depending upon the nature of the impregnating material and the conducting substance, the particular use for which the stencil sheet is designed, and the nature of the subject matter to be recorded thereon. The viscosity of the impregnating solution and the amount put in the sheet may be regulated by varying the proportion of volatile solvents or thinners used. Also, it will be appreciated that other ingredients may be substituted or added to give certain desirable properties to the completed stencil sheets, and that other substances which will be suitable equivalents for the purpose of the invention may be added or substituted for those given.

The flexibility of the method of producing stencil sheets of the character disclosed herein is demonstrated by the fact that in various instances commercial stencil sheets which are adequately plasticized may be employed by washing out the impregnation with acetone, ethyl acetate or other suitable volatile solvent and then adding to the impregnation the necessary amount of conducting material and reimpregnating the sheet with the conducting impregnation.

As to the degree of conductivity of the completed stencil sheet in accordance with the invention, this may vary within comparatively wide limits, the important feature being that the sheet be sufficiently conductive to pass the electrical signaling currents without offering undesirabl high resistance thereto and without causing the formation of destructive arcs which might burn or otherwise damage the paper base. Excellent results have been obtained by using alternating current signaling potentials of from 200 to 300 volts, at 2500 cycles, with marking currents of the order of from 20 to 30 milliamperes, although it is to be understood that the stencil sheet may be used with potentials lying outside the range stated and with other signaling frequencies and with other values of marking current. Also, the recording may be effected with direct current signals which may be either positive or negative as applied to the recording stylus.

Preferably, the stencil sheet is made as thin as practicable, although for certain purposes it may be desirable to employ thicker or heavier sheets. Stencil sheets prepared in accordance with the invention may be stored for long periods of time without showing deleterious effects from heat, light, moisture or other conditions to which they may be subjected, and they may be manufactured at a cost comparable to that of commercial stencil type-impressible sheets. Moreover, the details of reproducing copies therefrom, by the Mimeograph or other process, are the same as those of stencil sheets of commercial types currently in use, including the sponging ofi of the Mimeograph or other printing ink with the usual solvents preparatory to storage of the stencil for future use.

It will be understood that the invention is not limited to the examples or compounds described above, but that it broadly comprehends a stencil sheet adapted to be converted into a stencil by the application thereto of electrical signaling potentials, and having as its essentials a base, such as yoshino or other porous material, impregnated with a conductive impregnation which has the characteristic of being readily displaceable to expose the porous base in selected elemental areas of the stencil sheet in response to electrical signaling currents passed therethrough during a recording operation.

What I claim is:

An electrosensitive stencil sheet adapted for conversion into a stencil by electrical signaling currents applied to the sheet by means of a scanning stylus, said sheet comprising a fibrous base of porous open character, said sheet being impregnated with a stencil-sheet filling compound which is impervious to ink and when displaced defines the subject matter to be recorded, said impregnating compound having homogeneously embodied therein a conductive material in an amount to provide a path of sufficiently high conductivity that currents of approximately to milliamperes will flow by conduction through the stencil sheet when potentials of approximately 200 to 300 volts at 2500 cycles are applied by the stylus to said sheet, said conductive impregnating compound having a plasticity such that the hardness thereof, when calculated as a percentage from readings obtained b a Widney Modulimeter, is not less than approximately nor greater than approximately whereby the impregnating compound readily is displaceable by the passing therethrough of signaling currents of such amplitude and duration as will expose the fibrous structure of said base without appreciable damage thereto.

RETURN J. MEIGS.

REFERENCES CITED lihe following references are of record in the file of this patent:

UNITED STATES PATENTS Engler et al Apr. 18, 1944 

